Discrimination between poultry eggs on the basis of some observable quality is a well-known and long-used practice in the poultry industry. “Candling” is a common name for one such technique, a term which has its roots in the original practice of inspecting an egg using the light from a candle. As is known to those familiar with eggs, although egg shells appear opaque under most lighting conditions, they are in reality somewhat translucent, and when placed in front of direct light, the contents of the egg can be observed.
Eggs which are to be hatched to live poultry are typically candled during embryonic development to identify clear, rotted, and dead eggs (collectively referred to as “non-live eggs”). Non-live eggs are typically removed from incubation to increase available incubator space. In many instances it is desirable to introduce a substance, via in ovo injection, into a live egg prior to hatch. Injections of various substances into avian eggs are typically employed in the commercial poultry industry to decrease post-hatch mortality rates or increase growth rates of hatched birds. Examples of substances that have been used for, or proposed for, in ovo injection include vaccines, antibiotics and vitamins. In ovo treatment substances and methods of in ovo injection are described, for example, in U.S. Pat. No. 4,458,630 to Sharma et al. and U.S. Pat. No. 5,028,421 to Fredericksen et al.
In ovo injections of substances typically occur by piercing an egg shell to create a hole therethrough (e.g., using a punch or drill), extending an injection needle through the hole and into the interior of the egg (and in some cases into the avian embryo contained therein), and injecting one or more treatment substances through the needle. An example of an in ovo injection device is disclosed in U.S. Pat. No. 4,681,063 to Hebrank. This device positions an egg and an injection needle in a fixed relationship to each other, and is designed for high-speed automated injection of a plurality of eggs. The selection of both the site and time of injection treatment can impact the effectiveness of the injected substance, as well as the mortality rate of the injected eggs or treated embryos. See, for example, U.S. Pat. No. 4,458,630 to Sharma et al., U.S. Pat. No. 4,681,063 to Hebrank, and U.S. Pat. No. 5,158,038 to Sheeks et al.
In commercial poultry production, typically only about 60% to 90% of commercial broiler eggs hatch. Eggs that do not hatch include eggs that were not fertilized, as well as fertilized eggs that have died. Infertile eggs may comprise from about 5% up to about 25% of all eggs in a set. Due to the number of non-live eggs encountered in commercial poultry production, the increasing use of automated methods for in ovo injection, and the cost of treatment substances, an automated method for accurately identifying live eggs and selectively injecting only live eggs, is desirable.
There are other applications where it is important to be able to identify live and non-live eggs. One of these applications is the cultivation and harvesting of vaccines in live eggs (referred to as “vaccine production eggs”). For example, human flu vaccine production is accomplished by injecting seed virus into a chicken egg at about day eleven of embryonic development (Day-11 egg), allowing the virus to grow for about two days, euthanizing the embryo by cooling the egg, and then harvesting the amniotic fluid from the egg. Typically, eggs are candled before injection of a seed virus to facilitate removal of non-live eggs. Vaccine production eggs may be candled one or more days prior to injection of a seed virus therein. Identification of live eggs in vaccine production is important because it is desirable to prevent seed vaccine from being wasted in non-live eggs and to reduce costs associated with transporting and disposing of non-live eggs.
U.S. Pat. Nos. 4,955,728 and 4,914,672, both to Hebrank, describe a candling apparatus that uses infrared detectors and the infrared radiation emitted from an egg to distinguish live from infertile eggs. U.S. Pat. No. 5,745,228 to Hebrank et al. describes a candling apparatus that includes a photodetector and a photoemitter that are configured to be positioned on opposite sides of an egg. Light is generated in short bursts from each photoemitter and the corresponding photodetector monitors while it's corresponding photoemitter is operational. A flat of eggs is continuously “scanned” as it moves through the candling apparatus with each detector-source pair active while at least adjacent, and preferably all other, pairs are quiescent.
Unfortunately, commercial egg candling devices that utilize light (or egg opacity) to evaluate the condition of an egg usually operate in a dirty environment that can reduce the accuracy of such devices as the optical path is altered by debris and/or other materials that accumulate on the optical surfaces. Operators of machines using these candling devices may not have the training or motivation to keep these devices clean, and/or may not be able to easily access these devices to clean them. For example, a candling apparatus having a light source above moving flats of eggs and light detectors below the moving flats of eggs can have the detectors obscured by a fine layer of egg shell, chunks of egg shell, egg albumin, yoke or rotten innards, wash water, etc. Small accumulations of debris/material typically have a limited effect on the accuracy of an egg candling device. However, opaque materials like chunks of shell or rotten egg materials can reduce received light so that clear eggs may be interpreted by a candling apparatus as live eggs. Furthermore, accumulations of transparent materials, like albumin or water can act as a lens that conducts light reflected off adjacent eggs into the detector so that live eggs can be misinterpreted as being clear eggs. Exploding eggs, that are not uncommon, can spray both light detectors and light sources.